Stopped-flow spectrophotometric study on the self-redox reaction of some dithiophosphinates with copper(II)

The kinetics of the inner intramolecular electron transfer (or self-redox) reactions between two molecules of bis(disubstituted-dithiophosphinato)copper(II) complexes was studied by spectrophotometric stopped-flow technique in ROH/water. It was found that maximal absorption at 420 nm corresponding to the band of the initial complex is obtained at Cu(II)/ligand ratio 1:2. The kinetic runs following the decreasing absorption at 420 nm show that the reaction is second order in respect to CuII(R2-dtph)2 thus confirming the idea of an associate formation between two CuII(R2-dtph)2 molecules. The rate constant of the process strongly depends on the size and shape of the remote R substituents. The lower reaction rate at bulkier substituents is in agreement with the suggestion of hindered formation of the proposed associate. The rate constant also depends on the ROH/water ratio and on the nature of alcohol corresponding to the proposed reaction mechanism.